Studies on the Repair Defects of Ataxia Telangiectasia Cells
Patients suffering from ataxia telangiectasia (AT), a rare hereditary disease, show an elevated radiosensitivity extending from the clinical to the cellular level. Ataxia cells have been claimed to be deficient in repair of damage in DNA. Paterson et al. have developed a method to measure the number of γ-ray induced lesions in DNA of mammalian cells, by treatment with damage specific endonucleases (or glycosylases) present in extracts of Micrococcus luteus. With this method we studied the removal of these lesions in normal and AT3BI cells, but no difference in the rate of repair was observed.
We also studied the repair of γ-rays induced single-strand breaks. After moderate to high doses (2–15 krad), a rapid and slow repair could be distinguished, representing two different types of lesions. The induction of the rapidly repaired single-strand breaks could be prevented by the presence of cysteamine during irradiation. Both types of single-strand breaks were also observed in irradiated AT3BI cells; they were repaired at the same rates as in normal cells.
After low irradiation.doses (≤ 400 rad) in normal cells more than 50 per cent of the single-strand breaks was repaired within 2 minutes after irradiation, whereas preliminary results with AT3BI cells indicate that here some 3–6 minutes are needed to reach this percentage.
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